1. Field of the Invention
The present invention relates to a method of removing heavy metals from water (e.g. in environmental and biological samples) using highly porous hydrogel particles. More particularly, the present invention relates to a composition of matter for highly porous acrylonitrile-based micron- and submicron-sized hydrogel particles for use in remediation of soluble uranium ions in water (e.g. groundwater and wastewater) and as part of a system for measurement of uranium in environmental and biological samples.
2. General Background of the Invention
Uranium is a naturally occurring radioactive metal that occurs in low concentrations in nature. It is present in certain types of soils and rocks, especially granites. Naturally occurring uranium in groundwater is a result of the dissolution of uranium bearing minerals that have been in contact with groundwater for long periods of time. Elevated concentrations of natural uranium in well water are more likely to be found in drilled wells that obtain their water from the cracks and fractures of bedrock, rather than dug wells or surface water supplies. Uranium can also be found in the environment as a result of human activities such as mill tailings, emissions from the nuclear industry, the use of phosphate fertilizers and the combustion of coal and other fuels.
Naturally occurring uranium has very low levels of radioactivity. The chemical properties of uranium in drinking water are of greater health concern than its radioactivity. Most ingested uranium is due to food intake with lesser amounts accumulated from water or from the air. Most ingested uranium is rapidly eliminated from the body, however a small amount is absorbed and carried through the blood stream and deposited in the kidney, muscle and bone. Chronic exposure to uranium in drinking water is associated with altered kidney function without a clear threshold, which suggests that even low uranium levels can cause kidney damage. Current research shows that the safe concentration in drinking water may be close to the value promulgated by the U.S. Environmental Protection Agency, 30 parts per billion (ppb). Bathing and showering with water that contains uranium is not considered a health concern. There is inadequate data available to evaluate the carcinogenicity of ingested uranium.
The two most common methods of removing uranium from drinking water are reverse osmosis and ion exchange. Reverse osmosis works by force-driven water filtering through a membrane that prevents the uranium and other metals from passing through. Reverse osmosis systems require regular maintenance and quality monitoring and are fairly costly to implement. In addition, reverse osmosis systems do not specifically remove only one type of metal ion; they remove beneficial metals in addition to uranium.
One form of ion exchange works by passing water through a system that replaces uranium with a safer compound. Such ion exchange systems require regular maintenance and quality monitoring and are fairly costly to implement. Again, these systems are not specific to uranium but remove almost all the metal ions in the drinking water.
Another form of ion exchange involves the application of specific resins to the water supply. Ion-exchange resins are light and porous solids, usually prepared in the form of granules, beads, or sheets. When immersed in solution, the resins absorb the solution and swell; the degree of swelling is dependent on the polymeric structure and the total ion concentration of the solution. In industrial and domestic applications, ion-exchange resins are used for the removal of calcium, magnesium, iron, and manganese salts from water (water softening), for purification of sugar, and for concentration of valuable elements, such as gold, silver, and uranium from mineral ores. The ion exchange resins with specificity for uranium are very expensive, and require relatively long times (˜60 minutes) to remove uranium from environmental water samples.
The costs for the detection and measurement of uranium are presently high due to the complex methodologies required for analyses. Most analyses must be conducted in centralized facilities with costly instrumentation. The measurement of uranium thus requires transportation of the sample to the laboratory, and samples must often sit in long queues before analysis. Both of these factors lead to a significant delay between sample collection and analysis. There is an urgent need for lower cost, field portable assays that can provide reliable, near real-time data about uranium contamination at the contaminated site.
There is thus a need for more efficient and less costly methods of removing uranyl ions from water supplies and for measuring uranium in environmental and biological samples. The present invention meets these needs by providing a composition that is easily produced, yet is highly sensitive to uranyl ions. It removes uranium (uranyl ions) from water or other samples efficiently and effectively, while having a minimal effect on the other ions in the water sample. This composition can be used for treatment of water samples or as part of a test device to remove all the uranium from an environmental water sample. This treated water sample can subsequently be used as a control in the evaluation of water samples by an antibody-based test device. The present invention can be shown to be more sensitive and more effective than other compositions currently available.